The present invention relates to an electronic timepiece including a ROM address designation circuit and a RAM address designation circuit and more particularly, to an electronic timepiece using a Program Counter Method and Next Address Designation Method in the address designation of the ROM and a method for operating a value which extends over several words of the RAM as a single value by a single instruction.
In accordance with a remarkable expansion of digital electronic watch functions, microprocessor type LSIs for watches, i.e., LSIs of the type comprising ROM and RAM and a program written in the ROM is sequentially interpreted and executed for time counting and various controls while rewriting the value of RAM, have been put into a practical use.
This type of LSIs are expected to have increasingly sophisticated functions in accordance with an expansion in capacity of digital wrist watches as portable information instruments.
The instructions to be executed are stored in the ROM of this type of LSIs. There are two methods for designating the instruction address to be executed. One method is the "Program Counter Method" in which a program counter is employed, and the next address to be executed is designated by the content of the program counter. Incrementing of the program counter is automatically made in executing a certain instruction. The other method is the "Next Address Designation Method" in which a "field" of instruction of ROM is settled to designate all or a part of the next address to be executed. The program counter method is effective in constructing a software such as shown in FIG. 1, i.e., a software which is comparatively linear and which has less branches and judges. On the contrary, the next address designation method is effective in constructing a software such as shown in FIG. 2, i.e., a software which has many branches and judges. For determining which method is to be adopted for use in watch LSIs, a conventional software for watch has been analyzed. It has been found from such analysis that a software for watches belongs to that shown in FIG. 2. Namely, the software has many branches and judges and a numerical computation is simple. Accordingly, it seems effective to adopt the next address designation method for LSIs to realize the watch specifications. To realize a future multi-functioned digital wrist watch, however, it is desirable that LSIs can program a numerical computation. The numerical computation program is analyzed to be approximate to the software as shown in FIG. 1. It shows that it is effective to adopt the program counter method for LSIs which realize the specifications as numerical computation and shorten the word length of the ROM.
As illustrated, in view of the address designation of the ROM, it can be said that the software for watches includes the elements which are inconsistent with the software for the numerical computations.